1. Field of the Invention
This invention relates to a method for the treatment of microorganisms. More particularly, this invention relates to a method for the treatment of microorganisms which comprises subjecting the cell membrane of microorganisms to at least one chemical treatment with an acid, an alkali or a hydrophilic solvent prior to the mechanical rupturing of the cell membrane thereby making the cell membrane fragile and, with or without isolation of the thus treated cells, mechanically rupturing the cell membrane using a sand grinder or a three roll mill. The present invention aims at the improvement in the processability and digestability of the microorganisms and the removal of unpleasant odors inherent in yeasts by releasing or eluting proteins or other intracellular substances outside the cells.
2. Description of the Prior Art
At present, the proteins produced by certain microorganisms are considered to be the most promising means for solving the shortage of proteins in the world, and such microorganisms are generally cultured in a medium comprising a carbon source such as saccharides, hydrocarbons, alcohols, carbon dioxide and the like, a nitrogen source such as ammonia, nitric acid, urea and the like, as predominant components together with the requisite minerals and vitamins. The microorganisms which are known to produce proteins efficiently include yeasts, bacteria, green algae, blue-green algae and the like. However, these microorganisms usualy have a tough cell membrane and, therefore, it is very difficult to fully utilize the characteristics of the proteins since the enzymatic lysis of cells is extremely low and the foodstuffs produced from the cells containing such proteins, for example, a textured protein, an imitation milk or reformed products thereof in which a wheat flour, a corn flour, etc. is incorporated, generally tend to isolate the original mono-cellular microorganism when such foodstuffs are mixed into water.
In order to eliminate these disadvantages, various methods have hithertofore been proposed, for example, an alkali extraction method for extracting proteins from the microorganism at a pH higher than about 13 and at a temperature of 45.degree. to 65.degree. C. or more, or a cell membrane lysis method. However, these conventional methods tend to decrease the molecular weight of the proteins thereby reducing the usefulness of the proteins, and in addition the proteins obtained by these conventional methods lack good processability. Mechanical rupture of cells by an appropriate machine to extract enzymes has also been proposed, but, in this procedure, the rupture is not efficient and requires a prolonged time thereby resulting in the decomposition and/or denaturation of the proteins due to an endo-enzyme present in the microorganisms. For such reasons, mechanical rupture has not yet been practically utilized in the industrial production of proteins from microorganisms.